In an active-matrix type display device, e.g. a liquid crystal display device, thin film transistors are arranged as switching elements at pixels, and a tilt angle of liquid crystal is changed to transmit or block light, thereby displaying an image. When the liquid crystal display device displays a moving image, the characteristics of the liquid crystal make a user perceive that an image blurs without clear contrast. Such difference in perception is caused by afterimage effects of an image temporarily sustained in eyes of tracking a motion. Therefore, a user sees a blurred image because of a mismatch between movement of eyes and a static image of every frame even though the liquid crystal display device has a high response speed. To avoid such a motion blur in the liquid crystal display device, there has been used a method of driving the liquid crystal display device with a pulse width modulation (PWM) signal, i.e. an impulse signal by adding black data on to a screen after displaying video data on the screen. In this case, the PWM signal for reducing the motion blur has a frequency of 60 Hz and is applied by lowering a duty ratio up to about 25% so that the PWM signal can be delayed in time to fully open the liquid crystal.
However, flickering, i.e. a screen flicker occurs due to an impulse applied when the liquid crystal display device is driven with the PWM signal of 60 Hz.